The production of hydrocarbons often requires a borehole extending thousands of feet down into the earth, and that the hydrocarbons contained within a payzone be conducted into the borehole and up to the surface of the earth where the hydrocarbons are gathered. Most hydrocarbon producing wells require that a pumpjack be installed on the surface of the ground for reciprocating a string of sucker rod that extends downhole through the borehole to a downhole pump, so that the downhole pump lifts the formation fluid up through a tubing string to the surface of the earth. The downhole pump art is quite extensive and many clever engineers have spent a lifetime studying and working on downhole pumps of the type that are reciprocated by a pumpjack unit.
Various means for holding the pump apparatus downhole while the sucker rod string reciprocates part of the pump are known to those skilled in the art, and usually take the form of a seating nipple which is attached to the tubing string, and a pump hold-down which is sealingly supported in a removable manner in the seating nipple. Thus, the rod string can also be used to lift the pump hold-down from the seating nipple, thereby enabling repairs to be effected on the pump. It is well known that some pumps have a traveling barrel, while other pumps have a traveling plunger. There is no problem pulling a pump with the sucker rod string so long as it is not stuck downhole in the pump cavity or seating nipple. All that is required is time and money for the work-over rig and crew.
Some geological formations produce sand and other debris along with the production fluid. The sand and debris sometime become lodged between the seating nipple and the pump hold-down. When it comes time to pull the downhole pump, the sand and debris cause the pump to become stuck downhole, and the sucker rod string will break or part before it will lift the stuck downhole pump from the pump cavity of the borehole. A sucker rod string costs a lot of money, and can be ruined if it is overstressed and broken.
A stuck pump necessitates pulling the tubing string along with the rod string in order to replace the downhole pump. It is very expensive to pull the entire tubing string from a borehole, and in some instances where the tubing string is 8,000 to 10,000 feet long, the cost can amount to several thousand dollars. This is called "pulling a wet string", or a "stripping job", and is a detestable job for the roughnecks to endure, especially in the winter.
Many wells produce sour gas and salt water along with the crude oil. The pumps in these wells are stuck so often that they are almost always stripped of the rod string and tubing string whenever there is trouble with the downhole pump. The cost often causes the owner to shut-in a marginal well rather than endure the recurring cost of stripping the wet string several times a year.
The present invention provides method and apparatus by which a stuck downhole pump can be unseated and subsequently pulled from the borehole in a manner which avoids parting or over stressing the sucker rods, and which avoids the necessity of pulling the entire tubing string. This greatly reduces the cost of operation and allows a marginal well to be produced so that the hydrocarbons are made available to the public for many additional years.
The present invention is especially useful in conjunction with fiberglass sucker rod strings. Fiberglass rod strings are used predominantly where highly corrosive well fluids are encountered because the string is relatively inert and resists chemical reaction with the well fluids; however, the string has limited tensile properties and is easily parted. It follows that the present invention finds great utility in conjunction with a fiberglass rod string for a multitude of reasons, including the before mentioned ones, and others that will occur to those skilled in the art as this disclosure is more fully digested. This patent application is directed to one who is skilled in the art and such a person will understand the specifics of a downhole production pump, as for example an API RWTC type pump, API RWBC type pump, or a "tubing pump" of the type having a pump barrel incorporated as an integral part of the tubing string, with the pump plunger being lowered into the tubing on the bottom of the rod string. These production pumps are reciprocated by a rod string; and are provided with a hold-down of sorts which is received within a seating nipple of some arbitrary known design.